henrygusing up performance is your logging, not the actual registry access, which is basically free because the OS caches the value

My laptop is only capable of caching so much. Maybe a couple hundred registry values at once. And most of that cache is used up by the OS itself. And my other programs. Windows 10's inefficiency regarding registry spam is already reported to microsoft, though they threaten to take the same irresponsible stance on the issue as you just did. No program may thrash my registry just because it's cheap to do so at the moment. If everyone starts doing it, then it'll surely slow down. You expect it to be cached, but if every program relies on the cache, then it will quickly overflow. And then you pay the real, actually steep price for each registry access. Any instruction block is expensive when multiplied 300 times and that's just in one second.

Deleting or forbidding access to SDL2.dll as suggested by Mr. BEARDED ELECTRON is a good workaround until Valve addresses the issue in an acceptable manner.

I decided to eradicate it completely, replacing it with a blank file:PERMISSION DENIED on C:\Program Files (x86)\Steam\SDL2.dll (Size on disk: 0 bytes)

Bumbefly Sony Test I see you are still at it with your random knowledge base articles. They are not relevant to the issue at hand, sadly. This thread is about a specific registry key being erroneously spammed by design. No amount of reinstalling is going to fix that.

Thank you for the explanation of what is happening Mr henryg.

Edit: I have a controller. It does nothing in the UI (outside of games), so why does Steam insist on trying to capture its input? I especially do not need Steam to poll 300 times/second for my controller inputs, especially when it's not even plugged in. I rarely use it anyway. And even then I would prefer to let the game handle controller input, not steam.